<%@ page language="java" contentType="image/jpeg; charset=utf-8" pageEncoding="utf-8"
%><%@ page import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"
%>
<%@ page import="com.sun.image.codec.jpeg.JPEGImageEncoder"%>
<%@ page import="com.sun.image.codec.jpeg.JPEGCodec"%>
<%!
Color getRandColor(int fc,int bc){//给定范围获得随机颜色
Random random = new Random();
if(fc>255) fc=255;
if(bc>255) bc=255;
int r=fc+random.nextInt(bc-fc);
int g=fc+random.nextInt(bc-fc);
int b=fc+random.nextInt(bc-fc);
return new Color(r,g,b);
}
%><%
//设置页面不缓存
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","no-cache");
response.setDateHeader("Expires", 0);

// 在内存中创建图象
int width=60, height=20;
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

// 获取图形上下文
Graphics g = image.getGraphics();

//生成随机类
Random random = new Random();

// 设定背景色
g.setColor(getRandColor(240,250));
g.fillRect(0, 0, width, height);

//设定字体
g.setFont(new Font("Times New Roman",Font.PLAIN,18));

//画边框
g.setColor(new Color(255,255,255));
g.drawRect(0,0,width-1,height-1);

// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
g.setColor(getRandColor(190,200));
for (int i=0;i<255;i++)
{
int x = random.nextInt(width);
int y = random.nextInt(height);
int xl = random.nextInt(12);
int yl = random.nextInt(12);
g.drawLine(x,y,x+xl,y+yl);
}

// 取随机产生的认证码(4位数字)
String sRand="";
String[] sABC = {"a","b","c","d","e","f","g","h","i","j","k","l","m","n","p","q","r","s","t","u","v","w","x","y","z","1","2","3","4","5","6","7","8","9"}; 
for (int i=0;i<4;i++){
String rand=sABC[random.nextInt(33)];
sRand+=rand;
// 将认证码显示到图象中
g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));
//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
g.drawString(rand,13*i+6,16);
}

// 将认证码存入SESSION
session.setAttribute("rand",sRand);

// 图象生效
g.dispose();
// 输出图象到页面
//ImageIO.write(image, "JPEG", response.getOutputStream());
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(response.getOutputStream());
encoder.encode(image);

out.clear();

%>